Luteinizing hormone receptor binding inhibitor in aqueous extract of human corpus luteum

Aqueous extracts of human luteal tissue significantly inhibited binding of 125I-labelled human luteinizing hormone (LH) to the 2,000-g subcellular fraction of human corpora lutea. In contrast, aqueous extract of nonluteal tissue of the human ovary did not show a comparable activity to inhibit LH binding. Extracts of human corpus luteum had little or no ability to inhibit LH binding to porcine luteal homogenates. The inhibitory effect of the aqueous extract on LH binding to human luteal homogenate was demonstrated to be dose-related. The inhibitory effect of aqueous extracts of human corpora lutea on LH binding increased from the early to mid and late luteal phase of the menstrual cycle. The results of the present study suggest that there is an LH receptor binding inhibitor (LHRBI) in the 30,000-g aqueous extract of the human corpus luteum and the increase in LHRBI in the luteal tissue as the human corpus luteum ages may explain the means whereby the human corpus luteum regulates its own life span.